1. Field of the Invention
The invention is directed to an improved fuel injection valve for internal combustion engines.
2. Description of the Prior Art
A fuel injection valve of the type with which this invention is concerned is described, for example, in the patent application DE 100 31 265 A1 and has a valve body that contains a bore delimited its end oriented toward the combustion chamber by a valve seat that has at least one injection opening leading from it, which feeds into the combustion chamber of the engine in the installed position of the fuel injection valve. The bore contains a piston-shaped valve needle in a longitudinally sliding fashion, which has a valve sealing surface at its combustion chamber end, i.e. the end oriented toward the valve seat, and this valve sealing surface of the valve needle cooperates with the valve seat. In the closed position of the valve needle, i.e. when the valve needle is resting with its valve sealing surface against the valve seat, the injection openings are closed, whereas when the valve needle is lifted away from the valve seat, fuel flows between the valve sealing surface and the valve seat, through the injection openings, and from there, is injected into the combustion chamber of the engine.
The longitudinal movement of the valve needle in the bore is the result of the ratio between two forces: on the one hand, a hydraulic force that is generated by the pressure in the fuel-filled pressure chamber formed between the wall of the bore and the valve needle so that a hydraulic force is exerted on the valve needle. On the other hand, a suitable device that acts on the end of the valve needle oriented away from the combustion chamber exerts a closing force on the valve needle. The hydraulic force on the valve needle depends on the effective area that is acted on by the fuel, which yields a force component in the longitudinal direction. The opening pressure of the fuel injection valve, i.e. the fuel pressure in the pressure chamber at which the hydraulic force on the valve needle is sufficient to move it in the longitudinal direction away from the valve seat counter to an opposing closing force therefore depends, among other things, on the contact line between the valve needle and the valve seat, i.e. the so-called hydraulically effective seat diameter, because this affects the partial area of the valve sealing surface that is subjected to the fuel pressure. Wear between the valve sealing surface and the valve seat over the life of the fuel injection valve causes a change in this area, thus altering the hydraulically effective seat diameter. This also changes the opening pressure, which results in a changed opening dynamic of the valve needle. This also changes the injection time and injection quantity of fuel, which can lead to problems in modern, high-speed internal combustion engines, particularly with regard to fuel consumption and emissions.